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Unformatted text preview: cate over an analog transmission channel (say a telephone line).
When you want to use a modem with your computer to allow it to communicate
with any other computer via the telephone line, the following factors should be
1. Transmission speed
2. Internal versus external
3. Facsimile facility
4. Error correction
5. Data compression
They are described below.
1. Transmission speed. The higher is the transmission speed of a modem, the
better it is because it can communicate faster. The transmission speeds of earlier
modems were 300, 1200, or 2400 bps (bits per second). Although modems
having transmission speed of 2400 bps can still be purchased, you will not find a
new modem that is slower than this. For achieving transmission speeds higher than 2400 bps, many techniques are used
by modem manufacturers. In order to ensure that modems are inter-operable (can
communicate with another modem, even if it is made by a different manufacturer),
modems must conform to standards called modulation protocols. The standards for
higher transmission speeds for modems have been set by the Consultative
Committee for International Telephony and Telegraphy (CCITT). The first such
standard, called V.32, achieves transmission speeds of 9600 bps (four times the
speed of a 2400 bps modem). Another standard, called V.32bis ("bis" means in
addition to. Therefore V.32bis modems provide additional functionality to V.32
modems), allows modems to exchange data at a rate of 14400 bps. A more recent
standard, called V.34, allows modems to exchange data at a rate of 28800 bps.
Note that two modems can communicate with each other only if both follow the
same modulation protocol. That is, even if you have a modem that follows the
V.34 protocol, it cannot communicate at 28800 bps unless the modem on the other
end also follows the same protocol. To take care of this problem, most modems
are designed to have fall back feature. This feature allows a fast modem to
communicate with any slower modem. That is, when two modems attempt to
establish a co...
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- Spring '14